Meal recycling solvent extraction process



United States Patent MEAL RECYCLING SOLVENT EXTRACTION PROCESS 5 Joseph Pominski and Henry L. E. Vix, New Orleans, La.,

assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Application August 23, 1954, Serial No. 451,722

A non-exclusive, irrevocable, royalty-free license in the invention herein described, for all governmental purposes, throughout the world, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to solvent extracting vegetable oil bearing materials to produce vegetable oils and meals; the term meals being used to include any oil-free vegetable oil bearing material. More particularly, the inven' tion provides a method of recycling desolventized and dried solvent extracted meals to improve the filtration characteristics of oil-containing particles of vegetable oil bearing materials.

Vegetable oils and meals are relatively low cost products, and a successful solvent extraction process needs to be both rapid and efficient. Usually the vegetable oil bearing materials are hulled, cracked, and flaked to provide relatively small oil-containing particles which can be rapidly and uniformly penetrated by the oil solvent.

In many cases the filtration characteristics of the raw oil-containing particles are undesirably low. When some vegetable oil bearing materials are comminuted into small oil-containing particles they form many very small particles or fines i. e., particles varying from a size which will pass through a 300-mesh standard sieve to particles of a submicroscopic size. The fines tend to pack into an impervious mass from which solutions of the oil in the oil solvent drain ofi very slowly even when the drainage is conducted by means of vacuum filtration. Some oil bearing materials contain enough glutinaceous components to materially retard both the penetration of their oil-containing particles and the draining ofi of solutions of oil in the oil solvents.

Heretotore, to improve the filtration characteristics of oil-containing particles of certain vegetable oil bearing materials, the particles have been heated until the glutinaceous characteristics of their components have been decreased; but, in many cases, such a heat treatment alters the nature of the protein content of the oil-containing particles to such an extent that the meals yielded by the particles contain an appreciably lower proportion of soluble proteins than were bearing material. In some cases the oil bearing particles of high oil content vegetable oil bearing materials have heretofore been prepressed, to remove the bulk of their oil content, then carefully processed into thin flakes having an unusually high structural stability, to improve their filtration characteristics; but such processes require relatively costly specialized apparatus and a particularly careful control.

A primary object of the present invention is to provide a process of solvent extracting vegetable oil bearing materials to produce vegetable oils and meals, in which process the filtration characteristics of the oil-containing particles are materially improved without the necessary employment of any specialized apparatus or any heating in addition to that usually done in desolventizing the solvent wet oil-free particles produced by the contact with the oil solvent.

contained in the natural vegetable oil 2,729,661 Patented Jan. 3, .1956

In general, in accordance with this invention, vegetable oil bearing materials are solvent extracted by mixing oilcontaining particles of the vegetable oil bearing material with less than an equal weight, preferably from about 15% to 45% by weight, of desolventized and dried solvent extracted particles of a substantially oil-free meal yielded by the same vegetable oil bearing material; and solvent extracting the mixture. In general, the meal particles used can be obtained by substantially any method of solvent extracting the vegetable oil bearing material and desolventizing the solvent wet meal so produced.

However, the desolventized and dried meal particles used to dilute the oil-containing particles are preferably produced by heating solvent wet, substantially oil-free particles containing from about 8 to 20% of moisture on a fat free basis at a temperature of from about 145 to 230 F. in a dehydrative atmosphere until the particles are substantially free of solvent and have a moisture content of from 5 to 12%. The dehydrative heating that takes place when moist solvent wet'meal particles are so desolventized, case hardens the particles and produces friable particles which have a high filtration rate and which materially improve the filtration rate of mixtures of particles containing them. The desolventized and dried meal particles are preferably produced by a steam desolventization using direct steam heating.

The process of the present invention is adapted for employment as a continuous solvent extraction process. When it is so used, it provides a method of improving the filtration characteristics of the oil-containing particles of a vegetable oil bearing material that can be incorporated into a continuous solvent extraction process. In a process in which a vegetable oil bearing material is solvent extracted by comminuting it to produce relatively small oilcontaining particles, the oil-containing particles are contacted with an oil-solvent to dissolve the oil, and the solvent extracted particles are desolventized and dried, the filtration characteristics of the oil-containing particles are improved by desolventizing and dryingthe solvent extracted particlesby heating them while they are wet with solvent and contain from about 8 to 20% moisture on a fat free basis to a temperature of about 145 to 230 F. in a dehydrative atmosphere until the particles are substantially free of solvent and have a moisture content of from about 5 to 12% and continuously recycling a minor proportion by weight of the desolventized and dried particles by mixing them with a greater than equal weight, preferably from about 55% to 85% by weight, of the oil-con taining particles of the vegetable oil bearing mixture and solvent extracting the mixture. Where the solvent wet particles contain less than about 8% moisture they can be moistened by any of the usual methods of moistenin'g' vegetable oil bearing material particles. Where the solvent wct particles contain more than about 20% moisture the moisture content of the oil-containing particles is preferably adjusted so that the particles yield solvent wet particles containing less than about 20% of moisture upon being contacted with the solvent.

While, in general, there is a tendency for the fines to agglomerate into larger particles while the moist solvent wet particles are dehydratively heated in the desolventization and drying step, it is often advantageous to select the largervparticles of desolventized and dried meal as the proportion to be recycled. This relatively coarse fraction of the desolventized and dried meal can be isolated by the usual solid separating techniques such as screening and the like. The recycling of desolventized and dried meal particles having a size sufficient to prevent their passage through a standard mesh screen of at least aboutSO meshes per inch is preferred.

The process of this invention is adapted for the solvent extraction of oil bearing seeds having a relatively high oil content, such as cottonseed, peanuts, castor beans, sesame, fiaxseed, babassu nuts, and the like; as well as oil bearing seeds having a relatively .low content, such as soy beans, okra, tomato, and the like; and also :in the extraction of oil bearing materials other than oilseeds such as rice bran, wheat germ, corn germ, and the like.

While vegetable oil bearing materials can be extracted in accordance with the process of this invention in the form of particles of substantially any of the sizes and types heretofore used, the materials are preferably comminuted to relatively small oil-containing particles from which the bulk of the non-oil-containing contaminants have been removed. For example, the oilseeds are preferably hulled, cracked, and flaked to provide flakes having a thickness of less than about 0.016 inch. The hulling, cracking, and flaking can be accomplished by the use of the usual procedures and apparatus; and, if it is desirable, for example, in the case of oilseeds such as cottonseed, the hulled meats can be beat tempered i. c., heated to from about 140 to 190 F. at a moisture content of from about 6 to 12% for a few minutes prior to flaking. Such a heat tempering usually produces stronger flakes Without appreciable protein damage.

Where particularly high filtration rates are desired, the oil-containing particles to be mixed with desolventized and dried meals in accordance with the present invention can advantageously be rendered more friable and crisp by subjecting them to the mild moist cooking and crisping heat conditioning treatments more fully described in co- 0 pending applications, Serial Nos. 276,026, filed March 1]., 1952, and 314,234, filed October 10, 1952. In general, the heat conditioning treatments described in those applications comprise heating the oil-containing particles of the vegetable oil bearing materials to increasingly higher temperatures between about 170 and 235 F., with their moisture content controlled at between about 14 to 26% in the early stages of the treatment and' reduced during the remaining stages of the treatment. The heat treatment is continued for a time sufficient to render the oil easily extractable and to agglomerate fine particles, using conditions of temperature and moisture content causing a minor amount of protein damage. The hot, heat treated materials are then crisped by contacting them with a relatively cool atmosphere conducive to the evaporation of moisture until they undergo a uniform reduction in moisture content as well as in temperature.

The above copending applications describe solvent extraction processes in which the oil-containing particles which have been conditioned by the above described mild cooking and crisping treatments are extracted by a filtration-extraction technique.

In the filtration-extraction technique described in the copending applications, the conditioned oil bearing material particles are soaked in a relatively concentrated. miscella (an oil-solvent solution of oil) and then substantially freed of entrained miscella by means of vacuum filtration. In a preferred mode of operation, the soaking is accomplished by gently agitating the particles in contact with more than enough miscella to wet the particles. The slurry formed by the soaking is deposited on the bed of a continuous vacuum filter that is arranged so that particles on the filter bed can be washed by contacting the particles with a series of separate portions of liquids and separately filtering off and collecting the portions of liquids. The miscella in which the oil-bearing materials have been soaked is filtered off and sent to the solvent recovery system. The undissolved. oil bearing material particles remain on the filter bed and are subjected to a series of countercurrent washings with increasingly dilute miscellas, to substantially free them of entrained miscella. After a final washing with oil-free solvent, the substantially oil-free particles are removed from thefilter bed and sent to the desolventizer.

The process of the present invention can advantageously be used in conjunction with the filtration extraction technique.

When so used, the present process decreases the need for the mild cooking and crisping treatments which are usually used to impart an adequate filtration rate to the oil-containing particles. By improving the filtration rate of the oil-containing particles by means of the present invention, the intensity and duration of any cooking and crisping can be materially reduced and/or the filtration extraction technique can be applied to the solvent extraction of raw oil bearing materials or poorly developed oil bearing materials the oil-containing particles of which may not be susceptible to an adequate improvement in filtration characteristics by mild moist cooking and crisping.

in the solvent extraction of certain high oil-content oilseeds the present invention provides a particularly eflicient process in which the materials can be solvent extracted by a process in which they are subjected to very little heating. For example, the process of the present invention is particularly adapted for the solvent extraction of raw peanuts. Mixtures of raw peanut meats and dried desolventized peanut meal, which mixtures contain from about 15 to 45% of a desolventized and dried meal produced by heating solvent wet solvent extracted peanut particles containing from about 8 to 20% moisture on a fat free basis at a temperature of from about 145 to 236 F. in a dehydrative atmosphere until the particles are substantially free of solvent and have a moisture content of from about 5 to 12%, provide mixtures of oil-containing particles which have good filtration characteristics. The mixtures of oil-containing particles of vegetable oil bearing materials and desoiventized and dried meal can be solvent extracted using substantially any of the usual procedures and apparatus. The use of the ccuntercurrent extraction technique, and in particular, the use of the filtration-extraction technique is preferred.

Substantially any of the commonly used oil solvents for vegetable oil bearing can be used. Suitable solvents include hydrocarbons such as the pentanes, hexanes, and the like, and chlorinated hydrocarbons such as tetrachloroethyienc, and the like. The use of the commercial hexanes is preferred.

The following examples are illustrative of various details of the invention.

Using the laboratory scale filtration extraction equipment and technique described in J. Am. Chemists Soc, vol. 32, pp. l29l3l, 1955, comparative tests were made on the filtration characteristics of U. S. No. 1 Spanish peanuts. The peanuts were cracked and flaked to produce flakes having a thickness of about 0.01 inch, without heat tempering, using conventional cracking and flaking procedures and apparatus.

The filtration characteristics of the indicated mixtures of the peanut flakes with desolventized and dried peanut meal are summarized in the following table. In each case the desolventizcd and dried peanut meal was obtained by subjecting solvent wet hexane extracted peanut meal having a moisture content of from about 8 to 20% on a fat free basis at a temperature of from about 145 to 230 F. in a dehydrative atmosphere of saturated and superheated steam until the meal was substantially free of solvent and had a moisture content from about 5 to 12%. In the following table the peanut flakes are designated as raw i/I-l feed and the desolventized and dried meal is designated as dried meal. in each of the comparative tests the material to be extracted was first mixed with more than enough hexane to Wet the material and such a mixture was maintained for the indicated slurryiug time then drained free of liquid by means of vacuum filtration and' Washed until redraincdthe indicated number of times using; additional portions of hexane, until the material being extracted had been contacted with an amount of hexane providing the indicated ratio of solvent to weight of peanut meal.

Table Wt. raw P/N feed mixture, g 450 200 200 200 250 337. H1O in raw peanuts, percent 6. 6. 5 6. 5 6. 5 6. 5 1 8.8 Wt. of dried extracted meal feed mixture, g.- 0 150 150 1 150 113 62. 5 Ratio raw PIN to extracted PIN 4/3 4/3 4/3 2/1 5.4/1 Slurrying time, min 30 30 30 30 30 30 Number of washes 3 3 3 3 3 3 Vacuum, in. Hg 4 4 4 4 4 4 Solvent to peanut material ratio 1. 5/1 1. 9/1 1. 9/1 1. 9/1 1. 9/1 1. 70 Extraction temp., F. 73 78 145 78 80 140 Filtrate-mass velocity,

lbs./hr./sq. ft 112 3, 439 2, 840 410 1, 162 4, 130 Extracted cake:

H 0, percent 7. 2 8. 4 8. 3 6. 7 Lipids, percent 1. 37 0. 80 0.72 2. 46

1 Peanuts moistened from 6.5 to 8.8% 1120 before flaking.

I 300 g. mare, i. e., solvent damp extracted peanuts, containing 50% by wt. of solvent, which had not been dried.

From the data in the table it is apparent that in the test in which three parts of dried meal were mixed with four parts of raw flakes the filtration rate of the mixture was over 30 times greater than that of the raw meats. And, it is also apparent that when the filtration characteristics of the meats are improved in accordance with this invention, the overall efficiency of the extraction is equal to or greater than that of the usual filtration extraction processes. The lipids are reduced to about 1% by extracting a mixture of meats and meals at about 78 F. and at below 1% by extracting a similar mixture at about 145 F.

In addition, it is apparent that the solvent extracted material mixed with the meats to be extracted should be desolventized and dried. The mixture of 3 parts of mare and 4 parts of meats exhibited filtration characteristics which were not appreciably different from those of the raw meats.

We claim:

1. A process of solvent extracting a vegetable oil bearing material comprising: forming a mixture of oil-containing particles of the vegetable oil bearing material with from about 15% to 45% by weight of desolventized and dried, solvent extracted particles of a substantially oil-free meal produced by heating solvent wet solvent extracted particles of the same oil bearing material while they are wet with solvent and have a moisture content of from about 8 to 20% on a fat free basis to a temperature of from about 145 to 230 F., in a dehydrative atmosphere, until the particles are substantially free of solvent and have a moisture content of from about 5.0 to 12.0%; and solvent extracting the mixture to produce a vegetable oil and a meal.

2. In a continuous process of solvent extracting a vegetable oil bearing material by comminuting and flaking the vegetable oil bearing material to produce relatively small oil-containing particles, contacting the oil-containing particles with an oil solvent to dissolve the oil, and desolventizing and drying the solvent extracted particles by heating the solvent wet particles containing from about 8 to 20% moisture on a fat free basis at a temperature of about 145 to 230 F. in a dehydrative atmosphere until the particles are substantially free of solvent and have a moisture content of from 5 to 12%, the steps of improving the filtration characteristics of the oil-containing particles of the vegetable oil bearing material which comprise, continuously recycling a minor proportion by weight of the desolventized and dried solvent extracted particles by mixing them with from about to 85% by weight of the oil-containing particles of the vegetable oil bearing material, contacting the mixture of particles with the oil solvent, and desolventizing the solvent extracted particles.

3. The process of claim 2 in which the vegetable oil bearing material is peanuts and the oil solvent is hexane.

4. The process of claim 3 in which the minor proportion by weight of desolventized and dried solvent extracted particles which are recycled are particles having a size sufiicient to prevent their passage through a standard mesh sieve of at least about meshes per inch.

References Cited in the file of this patent UNITED STATES PATENTS 2,152,664 Rosenthal Apr. 4, 1939 2,608,565 Bonotto Apr. 26, 1952 2,629,722 Dunning Feb. 24, 1953 

1. A PROCESS OF SOLVENT EXTRACTING A VEGETABLE OIL BEARING MATERIAL COMPRISING: FORMING A MIXTURE OF OIL-CONTAINING PARTICLES OF THE VEGETABLE OIL BEARING MATERIAL WITH FROM ABOUT 15% TO 45% BY WEIGHT OF DESOLVENTIZED AND DRIED, SOLVENT EXTRACTED PARTICLES OF A SUBSTANTIALLY OIL-FREE MEAL PRODUCED BY HEATING SOLVENT WET SOLVENT EXTRACTED PARTICLES OF THE SAME OIL BEARING MATERIAL WHILE THEY ARE WET WITH SOLVENT AND HAVE A MOISTURE CONTENT OF FROM ABOUT 8 TO 20% ON A FAT FREE BASIS TO A TEMPERATURE OF FROM AOUT 145 TO 230* F., IN A DEHYDRATIVE ATMOSPHERE, UNTIL THE PARTICLES ARE SUBSTANTIALLY FREE OF SOLVENT AND HAVE A MOISTURE CONTENT OF FROM ABOUT 5.0 TO 12.0%; AND SOLVENT EXTRACTING THE MIXTURE TO PRODUCE A VEGETABLE OIL AND A MEAL. 